The landing site has been chosen for the European spacecraft that will touch down on the surface of Mars in 2003.

Beagle 2, which is being built by UK scientists and engineers, will land on Isidis Planitia, a large flat region that overlies the boundary between the ancient highlands and the northern plains of the Red Planet.

The area appears to be a sedimentary basin where traces of life could have been preserved - if it ever developed on Mars.

Beagle 2 is flying as part of the Mars Express mission, which includes an orbiting spacecraft that will investigate the planet's atmosphere and geology.

Low and smooth

"This is the best site given the landing constraints and scientific aims of Beagle 2," said John Bridges, from the Natural History Museum, London, who has been assessing possible landing sites.

Wishing for a happy Christmas 2003: Beagle 2 as it will look on the Red Planet

Isidis Planitia lies between 5 degrees and 20 degrees north. The target for Beagle 2 is close to 10 degrees north, near the maximum latitude possible for the craft to function properly in the cold Martian temperatures.

It is due to land on Mars in December 2003 during the northern hemisphere's spring. Detailed scrutiny of images of the surface suggests that the number of rocks on the surface is not large enough to threaten a safe landing.

The altitude of the site is also relatively low, which means the atmosphere should be thick enough to allow parachutes to brake the lander's descent effectively. The site also appears to have few steep slopes and does not seem to be too dusty.

Angle of entry

Sites previously under consideration included a channel south of Chryse called Simud Valles. It was said to be an interesting site but was too narrow to ensure a safe landing.

Another possibility was an area of the layered terrain that might have sedimentary rocks. "Unfortunately, this layered terrain is revealed in steep, narrow canyons which are unsuitable because of the landing ellipse size," John Bridges said.

The landing "footprint" is an area up to about 500 km (310 miles) long by 100 km (62 miles) wide. The size of the ellipse will depend on the angle at which the probe enters the Martian atmosphere, which has yet to be determined. The steeper the angle, the smaller the ellipse.

The site must be chosen to accommodate the maximum likely ellipse size and that rules out the bottom of many valleys. When it touches down, Beagle-2 will sniff the Martian air and drill into a rock to search for trace molecules of life.